Vacuum Packing is a method of preserving foods by preventing contact with oxygen - which is required by pathogenic and food spoilage microorganisms in order for them to live and multiply.

Vacuum packing sucks air out of food packaging so that there is no air around the food. It is used in the preservation of a wide variety of foods and is especially suited to smoked fish, sliced meat and poultry.

Vacuum packing can be achieved with the use of a commercially available vacuum sealer.

Vacuum packed foods may last longer than foods packed through other methods but you must remember that vacuum packing will only really control the amount of oxygen around foods and other environmental factors will continue to effect foods such as temperature, pH, moisture content, time and the amount of oxygen removed by vacuum packing.  Therefore, other methods of food preservation should be used alongside vacuum packing such as refrigeration or freezing if you are keeping the meat for a longer time - and you should also follow food specific guidelines regarding storage times.

Also called ROP (Reduced Oxygen Packaging); this technique creates an environment with low levels of oxygen which is required for growth of fungi and bacteria. It also prevents water being lost from the food.

It doesn’t prevent the growth of all types of microorganisms though. Some types of bacteria will multiply in an environment with low levels of oxygen. Some such bacteria (e.g. Botulism and Listeria), may thrive in vacuum sealed food, without causing any noticeable changes in the smell or visual appearance of the food.

Food products deteriorate faster when exposed to air. One benefit of canning or bottling is that air is largely eliminated from the food. Vacuum sealing is another and increasingly popular way of preserving meat and meat products.

The meat is normally placed in a plastic bag then a machine is used to extract all of the air from the bag, and seal it.

This technique is used by butchers and supermarkets to extend the use by date of fresh meat; but can also be used effectively in combination with other food preservation techniques.

 

What Containers to Use?

  • Plastic bag – specifically manufactured for vacuum sealing made of plastic or polypropylene (other plastic bags or ziplock bags are not suitable).
  • Glass jar - these come with a stainless steel lid that has a silicone seal for vacuum sealing; these lids create a water and air tight cover and are worth considering if you don’t like using plastic
  • Metal can – used in commercial production, but you can buy stainless steel cans that are a version of the glass jars mentioned above.

 

How Much Can Vacuum Sealing Extend Shelf Life?

Large cuts of meat or fish that may normally store in a freezer for up to 6 months; can store for up to 2 years in a freezer when vacuum sealed.

Ground (minced) meat, would only store roughly half that length of time, either way.

 

Types of Domestic Vacuum Sealers

There are two types of domestic vacuum sealers available: internal and external sealers and they both extract all the air and then use heat to seal a vacuum seal-able bag.

External versions seal the bag outside of the unit (only the bag opening goes into the sealer) use either clamping technology to seal the bag or a retractable nozzle. The air is removed from the bag as it is sealed. These are a great reasonable priced unit suited to infrequent home use.

The other type of sealer is a chamber type – in this unit the entire bag goes into the unit and it seals it very precisely and are therefore more thorough than the external units. They are also a lot more expensive and only really suited to very frequent, high volume, home use – for example if you are growing and processing your own meat on-site.

 

Things to Consider When Buying a Vacuum Sealer

  • Ease of maintenance and cleaning – some components of some units are dishwasher safe others are not
  • Types of bags the unit will accept: with some you can only use proprietary bags others will accept a range of bags including those purchased on rolls (which are cheaper)
  • Some units include external attachments that allow you will seal jars (such as Mason jars) and other suitable containers as well as bags. These may be more expensive but extend the unit’s usefulness and also means you can choose not to use plastic bags (if you prefer). These are usually a bit more expensive than the single use units but well worth considering if you are going to process a of food using a variety of containers and or bags.
  • Does it include an anti-drip tray? This is a must if you are going to process food that has a high liquid content (it prevents the liquid from getting sucked into the units accidentally).
  • Should you buy a unit with a double rather than single bar heating? The double seal is used when you need a greater strength in the seal. Single sealers are adequate for domestic use in most case
  • The length of the sealing bar – these can range from 12.5cm through to 40cm (for a commercial unit). They are also able to seal embossed or bags with channels as well as smooth plastic of various widths. Or you can seal two bags at once. The larger units are particularly suited to sealing bags containing meat.
  • Some models can also pump inert gases such as nitrogen into the bags using the nozzle – this is useful if you want to seal dried products such as nuts, coffee beans, potato chips and other fragile foods.

 

Before Sealing

Other than safety (discussed below) and what type of unit you prefer you also need to consider ageing, tenderness and flavour; these three considerations are directly associated with how the food is processed, the hygiene practices used, the freshness of the meat or fish, the quality of product, the proper storage conditions and knowing how to use the food later (reheating methods etc).

You don’t need to kill your own meat but always buy from a reputable butcher where you can see that the meat is fresh and hasn’t been stored or frozen beforehand. The fresher the meat the longer it will keep when vacuum sealed and frozen.

  • The meat should be thoroughly clean and dry before it is packed and sealed
  • Cut the meat (or fish) into serving size so you can vacuum pack into meal sized batches
  • If you want to store the meat for lengthy periods then it is a good idea to pre-freeze the meat for a short-term using freezer bags (24hours is long enough) and then seal it; long term freezing and the defrosting leads to excessive moisture and a loss of quality.
  • Place the meat flat in the bags
  • Some people also put an oxygen absorber which absorbs any oxygen left in the bag during processing
  • Use absorbent ‘mats’ or folded kitchen paper (on top of the meat) to soak up excess fluid so it doesn’t contaminate the seal before sealing
  • Make sure meat with bones haven’t compromised the bag – you may need to cover any jutting bones with kitchen paper or similar before processing
  • Whole poultry can be difficult to seal as air can remain trapped within the cavity; to avoid this pre-freeze the birds and then seal in the normal way and add an oxygen absorber too.
  • Label all the bags with the product and the date.
  • Use up fish within 4-6 weeks, chicken within 3 months and red meat within 6 months

 

What Dangers are there in Vacuum Sealing?

As in all preserving methods, and because all food borne pathogens grow with or without oxygen no preserving method is entirely safe.

Organisms grow at high temperatures but research has shown they also grow at low temperature in refrigerated conditions and can gradually reach quite high numbers along with the length of time the food is stored. It is all too easy to abuse temperature control in the home.

  • Low pH is also a contributing factor for vacuum processed foods.
  • Spore formers survive cooking even though most other vegetative cells are destroyed with both cooking and fermentation.

 

Preventative Steps

  • Always prepare food in scrupulously clean conditions – this includes personal hygiene as well as benchtops tools utensils and so on are all clean. Always wash your hands before starting
  • Avoid contact with your hands and food – use utensils or wear sterile rubber gloves
  • Don’t cross contaminate by using chopping boards, knives or any other utensils used in the process for more than one product. Never use the same utensils on raw and then cooked foods or visa-versa. Wash and scrub your tools, benches and boards (also in between processing as needed)
  • Only ever vacuum pack the freshest foods.
  • Store vacuum packed food in the fridge or freezer
  • All low acid food that have been vacuum sealed should be frozen
  • Consume foods straight after cooking
  • Make sure you have a complete seal (and that the seal is free of any refuse ) and label and date the food before refrigerating
  • Check the colour of the meat it should be a deep purplish colour not black, grey or brown which can indicate that it is contaminated.
  • Sealed meat will often have a strong smell upon opening – this should dissipate within 20 minutes or so – if not then you should not eat it. 

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